The present invention relates to mechanical presses, and in particular to a retracting bolster assembly which permits the die separation to be increased thereby affording easy access for maintenance purposes, and the like.
Mechanical presses, such as straight side presses and gap frame presses for stamping and drawing, generally comprise a frame having a crown and bed and a slide supported within the frame for reciprocal motion toward and away from the bed. The slide is driven by a crankshaft having a connecting arm connected to the slide, to which is mounted the upper die. The lower die is mounted to a bolster, which in turn is connected to the bed. Such mechanical presses are widely used for blanking and drawing operations, and vary substantially in size and available tonnage depending upon the intended use.
In most cases, the bolster is rigidly secured to the press bed and is not capable of any movement. This means that the maximum separation between the upper and lower dies cannot be changed without increasing the shutheight adjustment by raising the slide.
It is sometimes necessary to perform maintenance on the dies during a press run, but due to the fact that the stroke of the press is normally kept to a minimum for a variety of reasons, there is very little room for the diesetter to work on the dies while they are still in the press. This necessitates removing the dies from the press, which is quite time consuming and results in costly machine down time. In order to afford greater access to the dies while they are still in the press, the present invention provides a retractable bolster which can be dropped away from its normal, operational position.
Although certain prior art presses, both of the mechanical and hydraulic type, have been provided with bolsters and beds which are supported by means of hydraulic or pneumatic cylinders, this support is of a yieldable nature and functions as a die cushion, which yields to the downward force transmitted through the upper die and gives additional motion required in some press operations, such as blanking and drawing. The present invention, on the other hand, provides hydraulic support which is rigid and unyieldable to the downward force transmitted through the upper die, and in this respect functions no differently than a bolster which is rigidly connected to and supported by the press bed.
Some prior art presses are provided with safety bolsters, wherein an abnormally large downward force transmitted to the lower die due to die misalignment or a jammed part will cause the bolster to yield and be moved downwardly so as to relieve the abnormally large force thereby preventing jamming of the press. Such a device differs from the present invention in two respects. Firstly, safety bolsters are capable of only limited retraction, on the order of one-half to threequarters of an inch, and this is clearly not sufficient to enable access to the dies. Secondly, the retraction of a safety bolster is an automatic occurrence, as opposed to the present invention wherein the bolster is retracted by selective operation of a control actuator.